Dual-clutch transmissions having two clutches, whose input sides are connected to a drive input shaft and whose output sides are connected respectively to one of two transmission input shafts arranged coaxially with one another, are known in various versions. In these, one transmission input shaft is in the form of an outer, hollow shaft radially inside which the other transmission input shaft, in the form of a solid shaft, is arranged. Furthermore, in such a dual-clutch transmission it is known to arrange a drive output shaft coaxially with respect to the drive input shaft and to provide one or two countershafts. Such dual-clutch transmissions have the advantage that in a sequential series of gearshifts they can basically be powershifted, since in each case a gear associated with one of the clutches is active while a subsequent gear associated with the other clutch is pre-selected, and the gearshift is carried out by opening and closing the two clutches with a time overlap. In this way dual-clutch transmissions enable gearshifts to take place largely without traction force interruption and with a high level of driving comfort.
Dual-clutch transmissions are also known which have upstream splitter groups and/or downstream range groups, by virtue of which the number of gears in the main transmission can be multiplied. These group transmission designs are particularly appropriate for commercial vehicles, for example long-haul trucks, which on the one hand need a large number of gears with a correspondingly large transmission spread and on the other hand should provide a good level of driving comfort and high operational reliability. However, in transmissions designed in this way not all the gears can be powershifted. In particular, when—as is usual—the range group is designed to be shifted between two gear ranges, although it is true that most or all of the gears within the two gear ranges are made as powershift gears, the process of shifting between the range groups themselves cannot as a rule be carried out while maintaining the traction force. Moreover, since this shifting operation takes a comparatively long time, the gearshift in the main transmission and the shift in the range group, including the requisite synchronization processes, result, in the case of the gearshifts concerned, in on the whole lengthy shift phases in which the traction force is reduced or interrupted, these phases having a noticeably adverse effect on driving comfort.
From DE 10 2010 003 924 A1 a dual-clutch transmission is known, which has two transmission input shafts arranged coaxially with one another, a main shaft coaxial with and axially behind the input shafts, an upstream splitter group and a downstream range group. In this transmission two countershafts are arranged with mutually parallel axes. The range group is in the form of a simple planetary gearset in which the sun gear is connected to the output end of the main shaft and the planetary carrier is coupled on the output side to a drive output shaft. To engage a lower gear group with a short gear ratio in the slow range, the ring gear can be coupled to a positionally fixed component, and to engage an upper group with a direct transmission between the main shaft and the drive output shaft, the ring gear can be coupled to the planetary carrier. A radially inner one of the two transmission input shafts can be connected directly to the input end of the main shaft. On the main shaft is additionally arranged a hollow shaft on which at least one loose wheel of a forward gear is mounted to rotate, which loose wheel can be connected in a rotationally fixed manner to the main shaft by means of a shifting element. The hollow shaft can be connected by means of shifting elements to the main shaft and/or to the planetary carrier. The gears of this known transmission can at least predominantly be powershifted. In particular, by virtue of the connectable hollow shaft the range group can also be powershifted.
From the previously unpublished DE 10 2011 005 028 A1 a dual-clutch transmission which has two clutches is known, the input sides of which clutches are connected to a drive input shaft while their output sides are connected, respectively, to one of two transmission input shafts arranged coaxially with one another, and in which two countershafts arranged coaxially with one another and a range group are also provided. The two countershafts are respectively in the form of a hollow shaft and a solid shaft, with the solid shaft arranged radially inside the hollow countershaft. The clutches with the input shafts form in each case a partial transmission with a plurality of gears that can be engaged. The gears can be coupled to a drive output shaft via the associated countershaft of the partial transmission concerned and via a main shaft connected to a sun gear of the range group. The drive output shaft is positioned coaxially with the two transmission input shafts and is connected to a planetary carrier of the range group. On the input side, the planetary carrier is connected to a non-shiftable loose wheel of a wheel plane axially adjacent to the range group. The non-shiftable loose wheel meshes with a shiftable loose wheel arranged on the radially inner of the two countershafts. Thereby, at least one gear can be coupled to the drive output shaft independently of the range group. In this way a power path to the drive output is produced, which is independent of a range group shift so that all the forward gears can in particular one involving a range group shift in a sequential gearshift series be powershifted. With seven wheel planes, this dual-clutch transmission provides nine forward gears and two reversing gears.
From DE 10 2007 047 671 A1 a further dual-clutch transmission with two clutches is known, whose input sides are connected to a drive input shaft and whose output sides are connected, respectively, to one of two transmission input shafts arranged coaxially with one another. The dual-clutch transmission also comprises two countershafts arranged coaxially with one another and a range group in the form of a planetary gearset. The two countershafts are respectively in the form of a hollow and a solid shaft with the hollow shaft mounted to rotate on the solid shaft. By means of a shifting device that can be actuated on two sides, depending on the shift position of the shifting device, either the outer countershaft can optionally be connected to the inner countershaft in a rotationally fixed manner, or a loose wheel can be coupled, again in a rotationally fixed manner, to the inner countershaft. An element of the main group of the transmission, preferably a gearwheel, and an element of the range group of the transmission, preferably a planetary carrier, can be connected to one another by means of a coupling device. A drive output shaft is connected rotationally fixed to the planetary carrier. A gear of a lower gear range of the range group and a gear of an upper gear range of the range group can be formed at the same time, in such manner that the respective shifting clutches are closed but the associated powershift clutches, namely the input clutches of the dual clutch, are still open. The two transmission gears from the lower and upper gear ranges can also be engaged at the same time, in which case the powershift clutches are closed and the drive torque is transmitted in parallel by the gears in such manner that one of the two gears is selected, which then remains engaged, while the other transmission gear is disengaged. In this case a shift in the range group takes place under load.
A comparable dual-clutch transmission, but with two axis-parallel countershafts, is also known from DE 10 2008 036 165 A1.
Two further, similar dual-clutch transmissions, but respectively with one countershaft or with two countershafts arranged coaxially behind one other, are also known from U.S. Pat. No. 7,621,839 B2 and from U.S. Pat. No. 7,913,581 B2 respectively.